Program Director/Principal Investigator (Last, First, Middle): May, Gregory 1R01AI74673-01A1 Abstract Asperaillus fumigatus and other species are increasingly the cause of morbidity and morbidity amon~mmunocompromised patients. lnfeGons caused by these fungi are most prevalent in neutropenic patients with hematological malignancies. In the past few years'the echinocandin class of antifungal drugs, such as casiofungin, are increasingly being used to treat invasive aspergillosis (IA) a frequently life threatening disease that even with antifungal therapy has a mortality rate approaching 50%. Caspofungin and the other echinocandins are thought to act primarily through inhibition of beta-1,3-dglucan synthase. The use of caspofungin and related drugs in the treatment of IA will eventually lead to resistant isolates in the fungus Aspergillus fumigatus. To better understand how resistance to caspofungin is developed, we propose a combined genetic and molecular genetic study of the underlying mechanisms in the genetically tractable fungus Aspergillus nidulans. Additional genetic experiments will determine how other genes contribute to the caspofungin target pathway by isolating caspofungin sensitive mutants. The experimental aims will test the hypothesis that mutation in other genes will give rise to sensitivity to caspofungin. Caspofungin is believed to act through inhibition of the synthesis of beta-1,3-d-glucan a major component of the cell wall of veast and other funai. We hypothesize that aenes in other cell wall biosynthetic pathways act in synergy and mutations in these pathways can result in sensitivity to casuofungin. This genetic strategy will lead to additional candidate targets for devkloP6ent of new antifungals.- he genes identified in the genetic screens will be cloned and the site of the mutations identified. This will provide a molecular understanding of the nature of the cellular processes altered in the resistant and sensitive mutants. Identification of the genes will provide tools for future biochemical and cellular studies of the genetically identified processes. Proof that these same mechanisms operate in A. fumigatus will then be developed through molecular genetic manipulation of genes in this fungus.